Single Dad in Love(싱글파파는 열애중)

The love story of a single dad, Kang Poong Ho, who raises his 7 year old son alone after being abandoned by his first love, Yoon So Yi. By day he works as a pest exterminator and by night he is a martial artist. Jeon Ha Ri, is a medical student from a wealthy family who falls for Poong Ho. She secretly teaches Poong Ho's son, San, how to play the piano. Poong Ho's first love is also his son's mother who is a cold and proud woman who left her family to study abroad as a pianist. She was sponsored by Jeon Ki Suk who happens to be her fiancée and Ha Ri's father. Source (Drama Wiki)